from what i read in the past they work better without or defo not needed, tho i do have a groundplane kit stashed away , i think they look wrong being so short on the imax , and after all there only a99 top sections so i have plenty spare if my a99 breaks,when out mobile :-)

on air,tyne&wear,northumberland,durham,holy island,eu120+eu124 and anywhere from gateshead/north wales
scrap uk 40 give cbers L/M/Hcalling on 27.355/555 usb qsy 27.015 lsb/410 usb cb radio is for life not just for profits
i do cb radio not 11mtres,countrys worked 2015 with imax 2000 72

My Imax bends enough without adding a groundplane kit Warlock so have not tried one,but you could always make one out of thin wire,and that will have less surface area for the wind compared to the thickness of 4 top sections of an a99

You can talk worldwide on CB = not 10 - 15 miles,
some are too far up their own @rse to admit it = snobs,
but many freebanders just happen to know otherwise = test free.

From my understanding, if I was concerned about local contacts, the ground plane kit is beneficial. Although, apparently the radials are to short and you should make up longer ones. If DX is your main objective (of which there will be minimal due to the cycle 24/25 transition), then save your money for something else. There are so many variables to be concerned about as well.

Below is a link to my contact map that I achieved during the peak of last cycle with my IMAX 2000 at 12ft with no ground plane. I purchased the kit but never installed due to physical limitations. I was OK with the results.

Personally I would avoid any coax that is air spaced as it is susceptible to condensation within the spaces with varying temperatures and will fill with water, corrode and will in time find its way into the back of your radio. As for ground planes, these need to be a minimum of 8 feet 6 inches in length and fitted at an angle of 45 degrees, you only need 2 positioned opposite each other but 4 would be better.

I'm no expert on co-ax, but always thought the 9/10mm multi-core centre conductor in copper (less likely to suffer metal-fatigue and has more surface area for signals to wrap around the individual wires), with a solid insulator surrounded by a copper shield wrap, followed by a copper outer conductor with as little possible gaps in the diagonal-braiding as possible.

Technology has long since progressed, so this may be 30 years out of date, what with all the modern insulators and possibly things like silver plating on the copper etc

Again personally I say keep it simple, whatever you read about antennas it's all pretty subjective, work in fractions or multiples of the band you want to use it on, antenna, coax, ground planes and height above the ground, the rest will depend on your position, height ASL, lie of the land, what you have around you in respect of buildings, trees etc. Also a 1:1 SWR does not mean that you have the 'perfect' match, the optimum is, at the closest resonance to 50Ohms you can get will be about 1:4. Some will probably not agree but this is what I have found with the antenna system I use.